Voltage regulators are often used to provide an internal supply voltage to integrated circuits. Voltage regulators are typically designed to provide an adequate load current for the operation of a load circuit while at the same time providing a stable voltage to the integrated circuits. The integrated circuits whose power is supplied by the voltage regulator are oftentimes referred to as “load circuits” or, more simply, “loads.”
When in operation, each load connected to a voltage regulator typically draws a leakage current. Leakage current is the flow of current through unintended paths, for example through insulation layers within a load that have finite values of insulation resistance. In this regard, the total load current supplied to loads generally includes both the current drawn by the loads during normal operation and by leakage current of the loads.
One example of a load is a memory cell array, although any of a myriad of other circuit components may constitute a load. Although the amount of leakage current through each memory cell within a memory cell array is rather small, when thousands of memory cells are used within a memory cell array, the total leakage current of the memory cell array can become significant. Moreover, the amount of leakage of the memory cell array can vary depending on the operating temperature of the memory cell array.
Referring to FIG. 1, a chart 100 is depicted which presents an example plot 102 of the leakage current of a memory cell array vs. temperature, as well as other plots 104, 106 which will be described. It should be noted that the temperature values presented on the horizontal axis and the current values presented on the vertical axis are merely for explanatory purposes within the context of the present example. The respective scales may vary for different memory cell array implementations. Nonetheless, as depicted by the plot 102, the leakage current Ileak drawn by a typical load has a positive current-temperature coefficient. In other words, the amount of leakage current drawn by a load generally increases as the temperature of load increases. For example, the leakage current Ileak drawn when the load is very cold (e.g., −50° C.) can be very close to 0, but increase exponentially as the temperature of the load increases.
The variation in the amount of leakage current Ileak that is drawn by the load presents an issue when trying to maintain a stable supply voltage over a broad range of temperatures. Specifically, if the voltage regulator is designed to provide the proper supply voltage at a low temperature when the total current drawn by a load (i.e., operating current+leakage current Ileak) is low, the voltage regulator can become unstable, resulting in oscillations in the supply voltage. On the other hand, if the voltage regulator is designed to provide the proper supply voltage at a high temperature when the leakage current Ileak is at its maximum, the total power drawn from the voltage regulator may be well above the target power consumption level.
In one known voltage regulator, the temperature variation issue is addressed using an n-channel MOSFET (NMOS) transistor (commonly referred to as a “leaker”) that is electrically connected to the supply voltage in parallel with a load. This transistor will draw additional load current INMOS, for example as depicted in plot 104, from the voltage regulator when the total current drawn by a load is insufficient to keep the voltage regulator in stable operation, for example when the load is cold (e.g., −50° C.), and thus the leakage current Ileak is low, while the operating current also is low.
As noted, the leakage current Ileak of the load circuit generally increases exponentially with temperature. The load current drawn by the NMOS transistor also increases with temperature, but generally increases linearly. In consequence, the use of the NMOS transistor results in a greater total current Itotal, for example as depicted in plot 106, than is necessary when the load is at a normal operating temperature, and thus increases power losses.